So, the space available for my future aquarium purchase is limited to 33 inches wide. I was looking at a standard 30 inches wide and 18.75 inches tall 29 gallon aquarium, but then realized I could get a 37 gallon aquarium thats also 30 inches wide, but 22 inches tall, or even a 56 gallon aquarium thats 31 inches wide and 28 inches tall. Is there a big disadvantage to having a tank that deep? I know it might cleaning the gravel during a water change a little more difficult... but would it make a difference in the type of fish I could get?

Im not any expert but danios and tetras will be perfectly fine no problem and im sure the corys will be to just make sure the corys are getting food such as sinking pellets. And make sure the pellets are making it to the bottom.

This kinda tank would be PERFECT, if not to say a Angels dream. Angels would love to live in such a high tank.
The Cory will be fine. Now the Danios outta experience I have high doubts there, there's swimmers and then there's hyper active Danios....For them the good set up would a longgggg tank (rtaher 2x long then tall). So those I'd not chose for the high tank. A school of Tetra's (if your water permits as most pref soft & acidic water) would be ok IMO cause they're no where near the hardcore exercise then the Danios.

Ahhh and the planting options in a high tank...priceless......ideas ideas ideas here

~ Life Is Too Short, Break The Rules, Forgive Quickly, Kiss Slowly, Love Truly, Laugh Uncontrollably And Never Regret Anything that Made You Smile.
Life May Not Be The Party We Hoped For, But While We're Here, We Should Dance. ~

I have a 37 gallon and I love the look of it. However, it is a bit of a pain to clean. I'm up to my armpit to reach the bottom of the tank. Also, take into consideration if you'll be planting with live plants that stronger lighting may be needed to get enough light down to the bottom.

Depth does nothing for surface area. Surface area is the most important factor in terms of water surface area for air (o2) contact. Depth does nothing really except for fish that prefer depth such as angelfish. Depth will make light penetration less intense at the substrate level as well. In a low light tank the light reaching the bottom of taller tanks is less than shorter tanks. Wider and deeper (front to back) is better than narrower and higher. If you're not looking at getting fish like angelfish then I would go as wide and as deep (front to back) as possible.

Depth does nothing for surface area. Surface area is the most important factor in terms of water surface area for air (o2) contact. Depth does nothing really except for fish that prefer depth such as angelfish. Depth will make light penetration less intense at the substrate level as well. In a low light tank the light reaching the bottom of taller tanks is less than shorter tanks. Wider and deeper (front to back) is better than narrower and higher. If you're not looking at getting fish like angelfish then I would go as wide and as deep (front to back) as possible.

It appears I have been beaten to this. +1 If a tank of the higher variety is what you will choose, then make sure you have plenty of surface agitation.

I personally really like the 56 Gallon aquarium, I like that it is 18 inches deep and you can have a well planted tank that will maintain your fish. I personally don't like the narrower 12 inch tanks, even though they are certainly popular. Petsmart has a good deal on them right now and I think they'd make a terrific bedroom tank.